Spin valve sensors exploit changes in electrical resistance which occurs as a result of manipulating the relative orientation of the magnetization of ferromagnetic layers within a spin valve sensor. In conventional spin valve sensors, one ferromagnetic layer has its magnetization pinned while another, which has its magnetization set perpendicular to the pinned layer, is free to change its magnetic orientation in response to magnetized bits on an adjacent recording media. The magnetized bits on the recoding media, therefore, change the relative magnetization between the pinned layer and the free layer. An induced current through the spin valve is used to detect changes in the resistance of the spin valve that results from changes in the relative magnetization of the pinned and free layers.
The conventional spin valve utilizes an antiferromagnetic pinning layer adjacent the pinned layer to pin the direction of the magnetization of the pinned layer by exchange coupling. The free layer, which may be made of several layers, is separated from the pinned layer by a thin nonmagnetic metallic layer. The magnetic orientation of the free layer is aligned so that it is free to rotate in an active region.
The orientation of the free layer may set by an abutting biasing region as shown in U.S. Pat. No. 5,528,440, by Fontana et al., entitled SPIN VALVE MAGNETORESISTIVE ELEMENT WITH LOGNITUDINAL EXCHANGE BIASING OF END REGIONS ABUTTING THE FREE LAYER AND MAGNETIC RECORDING SYSTEM USING THE ELEMENT, issued Jun. 18, 1996, herein incorporated by reference in its entirety. Although such a structure allows the magnetic orientation of the free layer located between the abutting biasing regions to rotate, its structure is not easily fabricated at smaller geometries.
Smaller geometries are required to improve data density on the storage device. One way to improve data density is to reduce the track width of the data on the media. Reduced track width on the media requires a reduced track width reader to prevent inadvertent sensing of adjacent tracks or of other stray magnetic flux. Thus, as track width decreases, a smaller active region is necessary. Furthermore, as the active region becomes smaller, it is more critical that it have clearly defined boundaries. Therefore, a clearly defined active region is necessary for fabricating small read heads.
The present invention provides an exchange break to define the track width of the read head by selectively isolating an exchange coupling layer from an underlying ferromagnetic layer.
In the preferred embodiment, the exchange break is provided over a portion of the free layer of a spin valve device so that it inhibits exchange coupling between an overlying portion of the exchange coupling layer and the underlying free layer. The exchange break thus defines an active region of the free layer under the exchange break.
Although in some embodiments it is possible to form the exchange break of electrically conductive material, it is preferred to form the exchange break of an electrically insulating material to inhibit current shunting through the exchange break. The exchange break is preferably formed by depositing and etching an exchange break layer. As such, it also is preferred to form the exchange break layer of a material that is easily etched to minimize inadvertent etching of the underlying free layer and to ensure complete removal of the etched portion of the exchange break material layer.
It is possible to use a reentrant profile photoresist structure to define the exchange break. The exchange break may be formed under the photoresist structure with its edges generally aligned with the overhang portion of the reentrant photoresist structure. The exchange coupling layer then may be deposited typically forming drift portions under the overhang of the reentrant photoresist structure.
The drift portions often taper off and have a shifted material composition. These variations in thickness and material composition can degrade exchange coupling, blurring delineation of the active region of the free layer. The exchange break inhibits the drift portions from coupling with the underlying ferromagnetic material of the free layer, thus clearly defining the active region in this embodiment.
With some embodiments, a small amount of free layer material may be deposited just prior to exchange coupling layer deposition to establish good exchange coupling between the free and exchange coupling layers.
Because the width of the active region is defined by the exchange break, the present invention decouples the track width of the device from the geometry of the exchange coupling layer.